POST-GLACIAL HISTORY OF BOSTON. 459 



Bay and hence relatively fewer fossils. The very great change, 

 however, in the species represented, especially in the reduction both 

 in number of individuals and species, would seem to imply an 

 accompanying climatic change. That this refrigeration continued 

 during colonial days to the present is indicated by the disappearance 

 of oyster banks from the vicinity of Boston (Charles River, Mystic 

 Ri^•er and East Boston flats) and by the inability of planted oysters 

 to grow here now. 



5. A small thickness of sediment just beneath the "fiU" may be 

 due to the presence of dam walls built in the early part of the 19th 

 century. In 1814 a corporation, "The Boston and Roxbury Mill 

 Corporation," led by Uriah Coting, obtained a charter from the 

 General Court empowering them to build a dam from the end of 

 Beacon Street (at Charles Street) to Sewell's Point in the uplands 

 of Brookline, with a cross dam to Gravelly Point in Roxbury (see 

 dotted lines on map); also to made a roadway of each dam and to 

 levy tolls for its use. It could confine tide water within this area and 

 run mills by the water power thus created. At this time there was 

 nothing but water and salt marsh from the foot of the Common to the 

 uplands of Brookline. The mill dam was finished in 1821. But the 

 tidal power, rather insufficient at the beginning for the running of the 

 mills, was soon encroached upon, first, by the owners of bordering 

 property filling in their land, thus restricting the area of the dam; 

 and, especially, secondly by the building of the Boston and Providence 

 and the Boston and Worcester Railroads across the water basin 

 (these were incorporated in 1831). With this restriction of the tide 

 and the increase in population this basin soon became a public nuisance 

 and in 1852 a commission of the state legislature recommended that 

 the property be abandoned for mill dam purposes and be filled in 

 for building purposes. This was finally done, giving as a result the 

 topmost 15 to 20 feet in the above Back Bay sections. 



Man. — That man lived in this Boston region during the warmer 

 climatic period following the retreat of the glaciers is evidenced by the 

 excavation of the remnants of a fish-weir from these older sediments. 

 This was found in the subway excavation on Boylston Street between 

 Clarendon and Berkeley Streets, nearly opposite Rogers Building 

 of the Massachusetts Institute of Technology. This weir consisted 

 of interlaced vertical and horizontal sticks. The former were much the 

 thicker; one, when wet, had a diameter of over two inches, while 

 the latter in the same condition measured about a half inch. Some, 



